Ultra wideband (UWB) positioning architectures are known to typically involve two or more reference radios used to determine the position of a target radio. Conventional UWB positioning architectures determine the position of the target radio relative to the position of the reference radios. In these conventional architectures, each of the reference radios are generally placed at unique fixed locations and communicate signals with the target radio to determine the position of the target radio relative to the reference radios. Typically, the location of each of the fixed reference radios is determined by some independent method, such as global positioning system (GPS), local survey, or other known positioning or mapping systems. When determining the position of the target radio, UWB signals are communicated between the target radio and the reference radios. The distance between a given reference radio and the target radio can be determined from the time-of-flight of a UWB signal as the UWB signal travels between the reference radio and the target radio, where the time-of-flight can be measured directly or determined using various well known angle-of-arrival and/or differential time-of-arrival techniques.
However, known UWB systems suffer from various problems. Conventional systems do not allow for a quick addition of a new reference node to the positioning system. Typically, when a reference radio is placed in a UWB positioning system, the location of the reference node must be determined by a time-consuming independent method, such as GPS, prior to using the reference radio as a reference point. This may cause problems where setting up a positioning system is time critical, such as in firefighting or warfare. Additionally, conventional methods of determining the position of a non-fixed radio have insufficient accuracy and may have difficulty in resolving the position of a reference radio, particularly in situations when the radio is moving or which a GPS signal is blocked such as indoors. Moreover, traditional positioning architectures neither readily accept UWB radios nor incorporate their capabilities.
Additional problems in conventional UWB systems are caused by multipath characteristics of UWB signals. Multipath characteristics of a UWB signal impacts the accuracy of a time-of-flight distance measurement. Conventional time-of-flight distance measurements assume that the amplitude of a transmitted signal is received across a direct path between a transmitter and a receiver, and that the transmitted signal that follows the direct path is larger than received signals that follow an indirect path. Time-of-flight distance measurements also assume that the leading edge of the received signal corresponds to the direct path between a transmitter and a receiver. However, these assumptions are not always correct. Oftentimes, multipath signals may combine with one another such that the direct path portion of the signal has a lesser amplitude than combined multipath signals. Also, a direct path between two radios may not exist; in which case a time measurement based on a determined leading edge of a signal will not correspond to the direct path. In such a situation, a leading edge detection approach that assumes the leading edge corresponds to the location in the signal having the maximum amplitude may incorrectly determine the location of the leading edge. Incorrect determination of the leading edge results in error in the timing measurement, which translates into an incorrectly determined distance between the reference radio and the target radio that, when combined with other distance measurements between the target radio and other reference radios, further translates into an incorrectly determined position of the target radio.
What is needed, therefore, is an extensible positioning architecture that may quickly add additional radios to determine a position of a fixed or non-fixed radio with an acceptable accuracy.